I received three copies of The Times Killer Su Doku book as Christmas presents!

This book is causing me difficulties. The problem is that the introduction is ambiguous. The rules state

Quote:

The joined squares must be filled with numbers that total the printed number

It then goes on to cite examples, thus

Quote:

... in the case of three joined squares, if the printed number is 6, the only combination possible is 1, 2 and 3; ...

You can see the problem. If you accept the rule then there is not one combination possible, there are two, 1, 2 and 3, and 1, 1 and 4, this last possible with an L-shaped configuration over one or two box boundaries. If you accept the example, then the rule should have been modified to read

Quote:

The joined squares must be filled with different numbers that total the printed number

So I decided, in the interests of proving uniqueness, to follow the original rule, and allow any numbers in joined squares, including duplicates. So I worked through "Gentle", "Moderate" and "Tricky", completing puzzles 1–73. Some of these were very tough. There were no duplicates in joined cells. Unfortunately, I had not resolved the original problem, as the compiler could have saved duplicates in joined cells for categories "Tough" and "Deadly", irritating but possible.

I am now stuck on puzzle 74. After the trivial exercise of completing the two corner cells of the centre box, with their partners, I have come to a grinding halt. If you work to the modified rule then r6c3 can only be a 6. Working to the original rule there is no such obvious starting point; the whole puzzle seems to be too loosely defined, at least I cannot find any productive strategy.

I would be grateful for help with a strategy for this particular puzzle, allowing duplicates.

Also what are your views on The Times producing a book of this type, very obviously not properly tested on a reasonable sample of established Sudoku enthusiasts. I think it is sloppy, not what you expect from the world's most famous newspaper.

I've now finished all the puzzles in the book. As often happens with sudoku and its variants, the most difficult classification contains the most elegant and interesting puzzles. One of these is quite beautiful, with the solution route spiralling outwards from the centre.

Apropos my original query, all the puzzles in the book follow one set of rules, apart from No. 91, by a different author.